From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id A9AA46B06C8 for ; Fri, 9 Nov 2018 04:56:08 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id y23-v6so879104eds.12 for ; Fri, 09 Nov 2018 01:56:08 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p26-v6si365562edi.197.2018.11.09.01.56.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Nov 2018 01:56:07 -0800 (PST) Date: Fri, 9 Nov 2018 10:56:04 +0100 From: Michal Hocko Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c Message-ID: <20181109095604.GC5321@dhcp22.suse.cz> References: <20181109084353.GA5321@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: Kyungtae Kim , akpm@linux-foundation.org, pavel.tatashin@microsoft.com, vbabka@suse.cz, osalvador@suse.de, rppt@linux.vnet.ibm.com, aaron.lu@intel.com, iamjoonsoo.kim@lge.com, alexander.h.duyck@linux.intel.com, mgorman@techsingularity.net, lifeasageek@gmail.com, threeearcat@gmail.com, syzkaller@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Konstantin Khlebnikov On Fri 09-11-18 18:41:53, Tetsuo Handa wrote: > On 2018/11/09 17:43, Michal Hocko wrote: > > @@ -4364,6 +4353,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid, > > gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */ > > struct alloc_context ac = { }; > > > > + /* > > + * In the slowpath, we sanity check order to avoid ever trying to > > Please keep the comment up to dated. Does this following look better? diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9fc10a1029cf..bf9aecba4222 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4354,10 +4354,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid, struct alloc_context ac = { }; /* - * In the slowpath, we sanity check order to avoid ever trying to - * reclaim >= MAX_ORDER areas which will never succeed. Callers may - * be using allocators in order of preference for an area that is - * too large. + * There are several places where we assume that the order value is sane + * so bail out early if the request is out of bound. */ if (order >= MAX_ORDER) { WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)); > I don't like that comments in OOM code is outdated. > > > + * reclaim >= MAX_ORDER areas which will never succeed. Callers may > > + * be using allocators in order of preference for an area that is > > + * too large. > > + */ > > + if (order >= MAX_ORDER) { > > Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here? Because we do not want to blow up the kernel just because of a stupid usage of the allocator. Can you think of an example where it would actually make any sense? I would argue that such a theoretical abuse would blow up on an unchecked NULL ptr access. Isn't that enough? -- Michal Hocko SUSE Labs